Topic: Loose rubber o-ring thing - what is it for?

[kixbox]

Hi – hoping to get some help. I am in the process of cleaning my bike (CB750k 1978 – working on setting up a tracking blog under the Project Bikes section on the forum).
 
I wanted to get all the dirt from around the front chain sprocket and thought I’d check on the electrical under the shifter crankcase transmission cover. Curiosity got over me; I loosened and opened the shifter crankcase cover. All is good, cleaned and put back together no problem (I may need to go back there later this week to re-enforce the crankcase shifter cover gasket). 
 
Issue: when I was inspecting the little oil that came out before I put things back , I noticed this little rubber o-ring type (see picture). I tried to trace it back, looked at schematics, manuals for that area and can’t find a spot that uses something like this.
 


Would you happen to know what this is and where it should be? I’d like to replace it but can’t figure out what its for.
 
Thanks in advance.

Schematics I reviews:



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[flybox1]

#22?

https://www.cmsnl.com/honda-cb750k8-four-1978-usa_model7244/partslist/E++14.html#.Wx6ROdTwYdU

[ekpent]

 My schematic shows that o-ring #22 as an 11 x 2.5 mm so I would say Flybox may be on the money.

[kixbox]

Thanks for the quick reply!!

Hhmmm - it could well be actually. 

Though I would not have thought to check the crankcase schematics as I did not take off that particular cover (the one with the Honda logo). 

Do you think I should take it off? Is that where this ring would be?

If so, should I drain the engine oil? Any tips/precautions I should know about?

Thanks guys.





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[flybox1]

My schematic shows that o-ring #22 as an 11 x 2.5 mm so I would say Flybox may be on the money.

Couldnt tell you where it exactly goes tho...
I can only really remember one oring under the shifter cover, and its under the other transmission oiler/bearing pasageway....under the shifter mechanism/arm...

[flybox1]

Thanks for the quick reply!!

Hhmmm - it could well be actually. 

Though I would not have thought to check the crankcase schematics as I did not take off that particular cover (the one with the Honda logo). 

Do you think I should take it off? Is that where this ring would be?

If so, should I drain the engine oil? Any tips/precautions I should know about?

Well...the transmission is part of the crankcase...innit?     lol  the cover you removed exposes the shifter mech and trans... 

[kixbox]

Thanks for the quick reply!!

Hhmmm - it could well be actually. 

Though I would not have thought to check the crankcase schematics as I did not take off that particular cover (the one with the Honda logo). 

Do you think I should take it off? Is that where this ring would be?

If so, should I drain the engine oil? Any tips/precautions I should know about?

Well...the transmission is part of the crankcase...innit?     lol  the cover you removed exposes the shifter mech and trans...

Hahaha

Makes sense, daah

Thank again.  I’ll give an update.



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[kixbox]

I’m in my garage trying to plan how to get to no. 22.  To be honest, I’m at a bit of a loss. 

Looking at specs and manuals over one more time, could it be from the alternator cover (noticed three 11mm o rings on three cover screws)?



I would hate for it be the one inside the crankcase.  I think i would have to open the alternator and take everything off to get to the crankcase to replace the o ring assuming that is the way on.  Is that correct or is there a different way I’m missing?

It seems like a big job and I’m concerned that I could screw things up. 

[flybox1]

I’m in my garage trying to plan how to get to no. 22.  To be honest, I’m at a bit of a loss. 

Looking at specs and manuals over one more time, could it be from the alternator cover (noticed three 11mm o rings on three cover screws)? Not possible.  Those are washers... on the outside



I would hate for it be the one inside the crankcase.   It cant be from inside the crankcase, because the cases are sealed. I think i would have to open the alternator and take everything off to get to the crankcase to replace the o ring assuming that is the way on.  Is that correct or is there a different way I’m missing? It cant be from behind the alt cover....there are no orings in there....AND, its a separate, sealed compartment from the trans/shifter cover.

It seems like a big job and I’m concerned that I could screw things up.

Take off the shifter cover and have a look...take 3 good hi-res pictures of the area under it, and post them here.  we might see something

[MoMo]

The O-ring looks as though it had been there for quite some time,  from a previous PO maybe?   Still would be a good idea to do what flybox suggests

[kixbox]

The O-ring looks as though it had been there for quite some time,  from a previous PO maybe?   Still would be a good idea to do what flybox suggests

I think you are on to something - I think it must have been as the screws have some evidence of the clutch side being opened. 


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[kixbox]

So...I follow the reco:
- took the clutch cover off
- took the alternator cover off

I checked everything and it seems to me that everything is in place and in good order. 

There were no o rings inside the alternator cover - so it would seem that is not it (though I wished it was).

Pictures below of both. 










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[Progas]

I don't think it came from inside the cover, I actually think it's an oring from an O-ring chain! They fall out all the time and it got stuck to the back of your cover.

[kixbox]

I don't think it came from inside the cover, I actually think it's an oring from an O-ring chain! They fall out all the time and it got stuck to the back of your cover.

Just checked the whole chain and indeed I have missing orings - 4 in fact - and they look identical to the one I found - picture of one below. 

Now that I think about how I first noticed, I think you are right.  It was after I took the clutch cover off and it was stuck the cover side w the wires.  Probably my amateur error to think it came from inside. 

What do you think?

Leads me to another topic: is my chain okay?

I could not be more grateful to this community helping me along my journey.

Thank you

Here is where the bike is at now.





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[kixbox]

Side questions:

1)When I redo the gaskets for the two covers, should I apply Hondabind on the on the new gaskets?

2) a number of screw heads are shot and have a new CB750 sohc set, I am confused on what to use: should I apply loctite blue medium strength?

Thanks in advance.


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[MoMo]

I don't but maybe others do. I make sure all surfaces are clean and free from old gasket material. Never had a problem...Larry

[PeWe]

The o-ring might have fallen in from an earlier job? Under cylinder.
Item 22 is sealing the oil gallery plug just over the starter gear. The plug sits there.
I have attached a useful o-ring list.

[Progas]

I always put the gaskets on dry, make sure the surface is free of the old gasket and clean, as far as the screws, no locktite needed.

[flybox1]

I always put the gaskets on dry, make sure the surface is free of the old gasket and clean, as far as the screws, no locktite needed.

+1  Dry.

[kixbox]

Amazing - thank you for the help. 

- gaskets ordered (will put on dry)
- will not use locktite

thanks PeWe for the xls file (super helpful). 

[PeWe]

The o-ring xls file found on this forum.

One detail to verify is the o-rings to be used with the head gasket. Newer head gaskets can be thicker than old Honda. Thicker o-rings therefore needed. If thickness is increased the diameter which is Inner Diameter must be decreased since the Outer Diameter is the total of thickness x2+OD. 11x2.5=16mm OD.
Honda o-rings are nitrile wich I have got verified by ordering Viton that feel different, more plastic. Nitrile more like rubber and a little bit sticky.
Viton withstand high temp and chemicals better, but less support of cold temp compared with nitrile.

[kixbox]

Here is an update:

I received the new chain (630), and matching front and rear sprockets (old one had bad teeth).  Engine is currently off frame (frame was powdercoated).  Will likely start the LEGO build in a few weeks. 

Also, got all the gaskets (ordered OEM from Honda) and put on dry!! Fingers crossed all works well.

Have a problem with one screw (top screw on clutch cover). It just keeps turning and doesn’t lock/bottom out.  All others went in fine. I did not toque (more Thant 9ftlb). What do you think is the problem?

I checked I’m using the right length.  I tried to add some locktight. Nada, keeps doing it.  It may not be a big issue as all others are in place snugly, except this one. 

Thoughts?




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[MoMo]

threads most likely are stripped.  Try a screw a bit longer.  You may have to remove cover and run a thread chase through or have to helicoil

[Little_Phil]

threads most likely are stripped.  Try a screw a bit longer.  You may have to remove cover and run a thread chase through or have to helicoil

That's the danger of hex headed bolts. Originally JIS screw head. Tighten with good fitting driver, short tap with the manual impact, always fine. I'd say 6 ftlbs is fine here on threads that have been used a few times.
Be wary of using a longer screw unless you are certain that it will not bottom out. I've gotten away with using 35mm where 32mm was called up a few times, so there may be a few mm.
Otherwise thread insert

[kixbox]

I think I already tried a longer 35mm screw and same thing. 

Is helicoil same as thread insert?

This is 6mm, is it 1.0 pitch or something else?

Thanks gents



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